Release: OSL v1.12.7.1

Larry Gritz

We have tagged v1.12.7.1 as the latest production release and moved the
"release" branch marker to that point. This is guaranteed to be API,
ABI, and link back-compatible with prior 1.12 releases. Release notes
are below.

Note that this is a tweak release that only changes the build system.
If you weren't having trouble building OSL on your platform, there is
no pressing need for you to upgrade at this time.

Release -- 1 Dec 2022 (compared to
* Add clangSupport library as dependency to fix linker error on some
platforms. #1613
* Test against OpenColorIO 2.2. #1616
* Build: Fix how version overrides work to reduce the chance of user mistakes.

Larry Gritz